The present invention relates to a catalyst for use in a process for the simultaneous dehydrogenation and isomerization of paraffins to isoparaffins and isoolefins and method for preparing the catalyst and, more particularly, a modified mordenite zeolite catalyst containing Pt and a promoter.
Various processes exist in the prior art for converting paraffins to dehydrogenated and isomerized products. The dehydrogenated and isomerized products are particularly useful for the production of high demand products such as methyl, tertiary butyl ether (MTBE) and isobutylenes.
Heretofore the processes for dehydrogenation and isomerization of hydrocarbons have been developed independently following different paths. Dehydrogenation processes known in the art for the past 25 years have employed catalysts which comprise a noble metal, usually Pt, supported on a non-acid support, typically alumina or silica alumina. It is known in the prior art to further modify such a catalyst with one or two promoters so as to control the cracking of the hydrocarbon feedstock being subjected to the dehydrogenation process. Examples of catalysts of the type mentioned above are disclosed in U.S. Pat. No. 3,679,773; 4,000,210; and 4,177,218. Over the past ten years it has been the tendency in the prior art to increase the number of promoters used in noble metal catalysts so as to further reduce the loss of feedstock due to catalytic cracking. This tendency is clearly demonstrated in U.S. Pat. Nos. 4,381,257; 4,486,547; 4,880,764; and 5,012,027. The most commonly used promoters in the prior art discussed above have been selected from Groups IVA, VIB and VIII of the Periodic Table. These known prior art catalysts exhibit high activity, selectivity and stability for the hydrogenation of straight chain paraffins to straight chain olefins. The paraffin isomerization processes known in the prior art have generally been based on catalysts comprising noble metals supported on an alumina matrix and modified with chlorine, fluorene and ammonium. Examples of such catalysts are shown in U.S. Pat. Nos. 3,442,794 and 4,489,216. Recently, the prior art has employed zeolite supports in place of the alumina supports noted above. Zeolites, and particularly mordenite, have been used extensively due to the fact that they present no corrosion problems and have a high resistance to sulfur contained in the hydrocarbon feedstock. Examples of such catalysts are shown in U.S. Pat. Nos. 3,507,931; 3,551,353; 3,932,554; 4,400,576; 4,935,578; and 5,132,479. Further approaches have been tried for the isomerization of hydrocarbons using non-zeolite molecular sieves such as silica alumina phosphates as described in U.S. Pat. No. 5,132,484. All of the catalysts described above exhibit high activity, selectivity, and stability for the isomerization reaction while minimizing possible side reactions.
While the prior art discussed above have developed processes for the dehydrogenation of hydrocarbons and processes for the isomerization of hydrocarbons, few processes have been developed which are capable of the simultaneous isomerization and dehydrogenation of paraffin feedstocks to isoparaffins and isoolefins. The only process known to the inventors which is capable of simultaneous isomerization and dehydrogenation is described in U.S. Pat. No. 4,962,266 to Shum. The process described in the '266 patent employs a Pt based catalyst with zinc silicates. The drawback of the process of the '266 patent is loss of paraffins to side reactions which makes the process unattractive on a commercial basis.
Naturally, it would be highly desirable to provide an improved catalyst for the simultaneous dehydrogenation and isomerization of paraffins to isoparaffins and isoolefins wherein paraffin side reactions are limited.
Accordingly, it is the principal object of the present invention to provide a catalyst for the simultaneous dehydrogenation and isomerization of paraffins to isoparaffins and isoolefins. It is a further object of the present invention to provide a method for preparing a catalyst for use in the simultaneous hydrogenation and isomerization of paraffins to isoparaffins and isoolefins.
It is a still further object of the present invention to provide a process for the simultaneous dehydrogenation and isomerization of paraffins to isoparaffins and isoolefins employing a single catalyst.
Further objects and advantages of the present invention will appear hereinbelow.